New Emacs Guide - Emacs as a PHP Editor

I've updated the guides section with a new guide: How to set up Emacs as a PHP
Editor. There are some bits I'd like to add, such as how to manage PHP
projects, but it still contains some good information. I also added some new
Emacs snippets to the source code section of the site.

Whilst writing the guide I came across some new extensions I really like (such
as web-mode), so I've also updated the Emacs Extensions Guide.